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AZquotes claims that Lord Kelvin (or William Thomson) said this:

If you can not measure it, you can not improve it.

But there is no such a quote in his Wikiquote page. So did he actually say this?

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  • I haven’t checked whether other sources repeat this claim, but that doesn’t seem sufficiently notable.
    – Golden Cuy
    Oct 1, 2018 at 10:53
  • @AndrewGrimm how do you define sufficiently notable?
    – Ooker
    Oct 1, 2018 at 11:42

2 Answers 2

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He didn't say that exact quote; Lord Kelvin tended towards rambling, so if you see any particularly pithy one-liner quotes, it probably wasn't him. His actual quote?

I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be.

The actual source is from Antoine-Augustin Cournot, in De l’origine et des limites de la correspondance entre l’algèbre et la géométrie (1847), 375.

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  • how did you find the source?
    – Ooker
    Oct 3, 2018 at 10:48
-5

At here I found that:

When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be. often quoted as ‘If you cannot measure it, then it is not science’ Popular Lectures and Addresses vol. 1 (1889) ‘Electrical Units of Measurement’, delivered 3 May 1883

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  • 3
    This is the same quote provided in the accepted answer from 2018. Please make sure that you're not duplicating answers that have already been provided.
    – F1Krazy
    Dec 30, 2023 at 12:13
  • Although it is the same as the accepted answer has already, I would like to clarify that I found the earliest explanation of the quote on the webpage. Jan 5 at 7:40

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